The supply of fuel to all cylinders of an internal combustion engine may be interrupted during a mode of engine operation commonly known as deceleration fuel cut-off. U.S. Pat. No. 5,119,781 discloses a method of controlling engine fuel injection during transitional periods associated with deceleration fuel cut-off in order to interrupt the fuel supply to the cylinders.
Entry into the deceleration fuel cut-off mode may be initiated when the engine is decelerating, for example when the engine control element such as the throttle valve or accelerator pedal is positioned for engine idling. The deceleration fuel cut-off mode of operation may be used to reduce fuel consumption and maximize engine braking induced by the drag or negative torque applied by the engine load. Recovery from the deceleration fuel cut-off mode may be initiated when either the engine rotational speed drops below a predetermined minimum speed net idle or the engine control element is moved from the idling position to accelerate engine rotation and increase output torque. If an engine is quickly transferred from all cylinder operation to the deceleration fuel cut-off mode or vice versa, the sudden transition in engine output torque from positive to negative or negative to positive, respectively, may result in undesirable ringing or jerking in the engine driveline.
The output torque transients may be smoothed by gradually adjusting engine spark timing or the quantity of fuel injected into the engine during entry into and recovery from the deceleration fuel cut-off mode. However, both of these approaches have a negative impact on engine exhaust emissions because the amount of hydrocarbons present in the engine exhaust is increased.
Consequently, further improvements are desirable for controlling an internal combustion engine during entry and recovery from deceleration fuel cut-off. In addition, other improvements, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.